Ganon is the recurring villain in the Zelda video games made by Nintendo. Ganon is big and ugly. His first appearance was in the Legend of Zelda.
In the Legend of Zelda, Ganon can be defeated with any sword and any type of arrows. Hower, the Magic Sword and Silver Arrows will make the task easier since they do more damage. If you don't have a sword1 or don't have any arrows, you will not be able to defeat Ganon.
When you enter Ganon's room, he'll turn invisible. He teleports himself around the room, while shooting little magic balls at you. You must stab him with your sword repeatedly; this requires luck and patience since he's invisible and teleports. When you hit him, he'll become temporarily visible and blue. Eventually, you'll hit him and he'll become visible and red. When he's red, then you need to hit him with the arrows. If he doesn't die, he'll go back to being invisible and teleporting.
1: It is possible to get to Ganon without acquiring a sword, although this requires a lot of patience. Sadly, it is not possible to win the game this way since the sword is needed at the very end to defeat Ganon.